Green’s Dictionary of Slang

1. the penis.

1748–49		Cleland Memoirs of a Woman of Pleasure (1985) 162: My fingers too had now got within reach of the true, the genuine sensitive plant.
1779		Mimosa: or, The Sensitive Plant 9: This plant, enrich’d with sense and life, / Pleases the widow, and the wife.
1779		Nocturnal Revels 2 187: She espied through a bush a most extraordinary Sensitive Plant, which her Grace soon discovered to be Tit Tit’s [i.e. the nickname of one Mr Toy] .
1784		Rambler’s Mag. June 226/1-2: The tree of life is a succulent plant consisting of one only straight stem [...] The stem seems to be of the sensitive tribe, though herein differing from the more common sensitives, that whereas they are known to shrink, and retire from even the gentlest touch of a lady’s hand, this rises [...] and extends itself when it is so handled.
1788		Harris’s List of Covent-Garden Ladies 124: [She] particularly likes Adam’s apple-tree, sensitive plant, stich-wort, nutmegs and such valuable productions.
[1788		Harris’s List of Covent-Garden Ladies 48: She loves to restore the drooping plant].
1857		Venus’ Miscellany (NY) 31 Jan. n.p.: My pants all open in front and my ‘sensitive plaything’ exposed.
c.1890		‘The Frozen Limb’ in Voluptuous Night (Horntip Coll.) 95: We kept melting and freezing, and Mary kept squeezing / My sensitive plant all the night till daybreak.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1928–32		in G. Legman Limerick (1953) 15: There was a young lad from Nahant / Who was made like the Sensitive Plant. When asked, ‘Do you fuck?’ / He replied, ‘No such luck. / I would if I could but I can’t.’.

2. (orig. boxing) the nose.

1825		Pierce Egan’s Life in London 17 July 197/2: Tom countered his adversary on his sensitive plant.
1832		Egan Bk of Sports 25: The sensitive plant of the Oxford Scholar received a small taste.